No. 2.] PHYSIOLOGICAL MORPHOLOGY. 25$ 



eggs. At 10.20, before any segmentation, even in the normal 

 sea-water, had taken place, I took a lot of eggs out of the con- 

 centrated solution and brought them back into normal sea-water. 

 At 10.33 these eggs began to segment. The segmentation was 

 a normal one, as only segmentation into two cells took place. 

 At the same time segmentation had taken place in nearly all 

 of the normal eggs. The only difference between the normal 

 eggs and the plasmolyzed eggs was that the former at 10.33 

 were nearly all segmented, whilst of the latter only a small 

 part had undergone segmentation. Ten minutes later, however, 

 every second one of the plasmolyzed eggs was segmented mostly 

 into two, exceptionally into four, segments. But now the situa- 

 tion began to change. By this time, the normal eggs began to 

 reach the four-cell stage, and now many of the plasmolyzed 

 eggs which had not yet segmented into two cells began to 

 segment into three or four cells at once, without going through 

 the two-cell stage at all. The cleavage took place in this way, 

 — that at the same time, or shortly after each other, spherical 

 projections appeared on the surface of the Qgg, which at first 

 were coherent, but which soon, at the same time or in quick 

 succession, were separated. This kind of segmentation seems 

 to be identical with that kind which O. and R. Hertwig observed 

 under other circumstances, and have described as " Knospen- 

 furchung."^ The further segmentation was the same in the 

 plasmolyzed and in the normal eggs. 



At 1 1 o'clock I brought a second lot of eggs back from the 

 concentrated solution into normal sea-water. These eggs did not 

 show the slightest trace of segmentation. At 11.22 the eggs 

 began to segment, but in hardly any case did the egg divide 

 into two, but nearly all of them segmented into more cleavage 

 spheres at once. The number and size of the cleavage spheres 

 was not quite regular. There were mostly about four spheres 

 in one egg, sometimes, however, five to eight. The size of the 

 single cleavage spheres of the same egg varied, the smallest 

 spheres being about the size of a cleavage sphere of the eight- 

 cell stage, the largest that of a two-cell stage. At 11.44 the 

 first segmentation was finished, and from now the segmenta- 

 tion was perfectly regular. At 11.40 the normal eggs were in 

 the eight-cell stage. 



^ O. a. R. Hertwig, Ueber den Befruchtungs- und Teilungsvorgang des tierischen 

 Eies unUr dem FAnJluss dusserer Agentien. jfen. Zeitschr., XX, 1887. 



